1. Field of the Invention
The present invention relates to a substrate structure and a process thereof. More particularly, the present invention relates to a substrate having a blind hole and a method for forming the blind hole.
2. Description of the Related Art
FIGS. 1 to 3 show schematic views of steps of a conventional method for forming a blind hole in a substrate. In FIG. 1, firstly, a substrate 1 is provided, and the substrate 1 includes a lower dielectric layer 11, a copper layer 12, and an upper dielectric layer 13. The copper layer 12 is located between the lower dielectric layer 11 and the upper dielectric layer 13. The upper dielectric layer 13 has an upper surface 131, and the copper layer 12 has an upper surface 121. Under normal circumstances, the substrate 1 further comprises a copper layer (not shown) which exists on the upper surface 131 of the upper dielectric layer 13. The materials of the lower dielectric layer 11 and the upper dielectric layer 13 are generally epoxy, phenolic, or polyester.
Next, in FIG. 2, a blind hole 132 is formed by processing the upper surface 131 of the upper dielectric layer 13 downward by laser processing or chemical etching, and the blind hole 132 penetrates the upper dielectric layer 13 and exposes the upper surface 121 of the copper layer 12.
Finally, in FIG. 3, an electroplating copper layer 14 is formed on the side wall of the blind hole 132 or is filled into the blind hole 132, so as to electrically connect the copper layer 12 and the copper layer on the upper dielectric layer 13.
FIG. 4 shows a schematic view of the conventional substrate having a blind hole under thermal test. The conventional method for forming a blind hole has the following disadvantages. In the substrate 1 having the blind hole 132 made by the above method, since the joining interface of the copper layer 12 and the electroplating copper layer 14 is poor, when the substrate 1 undergoes the thermal test (including thermal cycle test (TCT) and thermal shock test (TST)), a crack 15 is generated in the electroplating copper layer 14 during the temperature change. The crack 15 extends upward from the bottom of the blind hole 132 (i.e., the connecting surface of the copper layer 12 and the electroplating copper layer 14). The crack 15 causes an open circuit between the copper layer 12 and the electroplating copper layer 14, thus reducing the reliability of the substrate 1.
Therefore, it is necessary to provide a substrate having a blind hole and a method for forming the blind hole to solve the above problems.